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41 million years ago, when the continents of Africa and South America were closer together, storms sent clumps of floating vegetation down rivers and into the Atlantic Ocean, and currents carried this debris from Africa to South America. The ancestors of American monkeys and caviomorph rodents rafted on this debris and eventually colonized their new home. The caviomorph rodents radiated and evolved into many different species including cavies, agouties, chinchillas, hutias, capybaras, and porcupines. South and Central America are home to 16 different species of porcupine in the coendou genus, but just 1 species lives in North America. The scientific name for the North America species of porcupine is Erithizon dorsatum. The ancestor of E. dorsatum crossed into North America when Central America emerged above sea level, but until recently scientists knew little about it. Scientists did have fragmentary evidence of this evolutionary ancestor, and they named the species E. poyeri. However, a few years ago, a nearly complete skeleton of E. poyeri was found at a fossil site located in north central Florida known as Haile 7G. The specimen is estimated to be 2 million years old. Scientists were able to study this specimen in detail, and they found this animal had physical characteristics that showed it was an evolutionary link between North and South American porcupines.

Photo of a North America porcupine. It is larger and has different shaped teeth and jaws than South American porcupines.

Photo of South American porcupine. They have prehensile tails. Modern North American porcupines do not, but the evolutionary ancestor of North American porcupines did.

Specimen of the evolutionary ancestor of North American porcupines. It had physical characteristics resembling North and South American porcupines.

South American porcupines have prehensile tails that can wrap around a tree limb and completely support their weight. Modern North American porcupines don’t have prehensile tails, and their tails are shorter, but E. poyeri did have a prehensile tail. The shape of E. poyeri’s jaws and teeth did more closely resemble those of modern North American porcupines. They were adapted for eating more inner bark (cambium) than South American porcupines eat, and this adaptation enabled them to range into regions with harsher climate. They also evolved to grow to a larger size to help them retain more body heat–another adaptation to colder climate. Today, porcupines are absent from southeastern North America. This may be because they reproduce slowly and can’t endure intense human hunting pressure. Their quills protect them from inexperienced predators but afford no protection from a human who can just walk up and hit them over the head with a club. They can survive in areas with sparse human populations that have lost their taste for porcupine. Porcupines originally colonized southeastern North America when a corridor of forested habitat occurred along the Gulf Coast connecting this region with Central America.

Reference:

Vitek, N.

“An Extinct North American Porcupine with a South American Tail”

Current Biology 34 (12) 2024

The Rancho La Brea Tar Pits in California are a unique and valuable fossil site. Most fossil sites yield more specimens of herbivores than carnivores because in a normal ecosystem the former greatly outnumber the latter. When carnivore remains are found, they usually consist of isolated bones or teeth. But the tar pits served as a trap that captured a greater number of predators that were attracted to flailing herbivores stuck in the tar. The specimens that are found are often large sections of the skeleton. Scientists learned more about saber-tooth cats from the thousands of specimens found here than from any other site in the world. Among the interesting specimens are the mostly complete skulls of juvenile saber-tooth cats. Scientists were able to study the baby teeth of saber-tooths and learn how adult fangs developed.

Saber-tooth skull with baby fangs and unerupted adult fangs. The 2 stabilized each other when the cubs were learning to bite, thus preventing damage.

The milk teeth and unerupted fangs helped stabilize each other and prevented tooth breakage while the cats were inexperienced. The way the teeth developed reduced the chances the teeth would be damaged before the cat learned how to properly bite its prey’s throat. It took longer for saber-tooth’s canines to develop than it does for other big cats–the eruption period was prolonged. The erupted canines didn’t replace the milk teeth until saber-tooths were 30 months old. This is about how long it took before their powerful forelimbs were strong enough to hold prey down, so a killing bite could be administered with less risk of traumatic injury to the canines.

Some scientists believe saber-tooths were social animals, but I disagree because they had smaller brains than lions. I don’t think they lived in packs. However, I do hypothesize they lived in family groups, and cubs stayed with their mothers for 2-3 years. Mother cats and nearly full-grown cubs likely hunted larger prey as a team.

References:

Tseng, Z. Jack

“Bending Performance Changes during Prolonged Canine Eruption in Saber-toothed Carnivores: A Case Study of Smilodon fatalis”

The Anatomical Record Special Bulletin April 2024

Wysocki, M.

“Fossil Evidence of Evolutionary Convergence in Juvenile Dental Morphology and Upper Canine Replacement in Saber-tooth Carnivores”

Ecology and Evolution October 2019

A new study of isotopic carbon from Pleistocene bison tooth enamel suggests bison had a more flexible diet than previously thought. Bison crossed the Bering Land Bridge about 190,000 years ago and colonized North America. Bison were formerly thought to have arrived in North America 240,000 years ago, marking the beginning of the Rancholabrean Land Mammal Age, but genomic studies combined with the known timing of the formation of the Bering Land Bridge and paleontological evidence suggests they arrived more recently. The species of bison that colonized North America is known as Bison priscus. This species gave rise to the largest species of bison in history–Bison latifrons, an animal that thrived during the Sangamonian Interglacial (132,000 years BP-118,000 years BP) and the early part of the Wisconsinian Ice Age until about 24,000 years ago. Bison latifrons likely evolved into Bison antiquus, a smaller species that lived during the coldest stage of the last Ice Age. In turn Bison antiquus evolved into a still smaller species, the modern Bison bison. Bison occidentalis is thought to be a transitional species between B. antiquus and B. bison. Fossils of this species have only been found in western states. Scientists thought Pleistocene bison were grazers that mostly ate grass, but this new study finds they actually ate a variety of plant foods and could be considered mixed feeders.

Image of all the known bison species that have inhabited North America over the past 190,000 years. They all likely evolved from Bison priscus.

The scientists who authored the below referenced study analyzed the carbon isotopic ratios found in the teeth of 32 specimens from 4 different regions of North America plus previously published data from 142 specimens. The teeth came from specimens excavated from sites including Snowmass, Colorado, the American Falls Reservoir, Idaho, and Diamond Lake, California. They also looked at specimens from 5 sites in Florida–Haile, Bradenton 51st Street, Auffenberg, Withlacoochee River, Ichetucknee River, and Millenium Park. Specimens from the California and Colorado sites showed a seasonal variation in diet, but the specimens from Florida and Idaho show these animals ate the same diet year-round. Bison living in Snowmass, Colorado during the Sangamonian Interglacial enjoyed a climate and environment similar to today–it was mostly pine and spruce surrounding a marsh. However, 10 species of plants not found there today did occur there then. About 87,000 years ago this area transformed into a drier grassy steppe environment. Semi-aquatic mastodons were replaced by upland Columbian mammoths. The site in Idaho also hosted an environment similar to that found in the area today, though 1 species of fern from the last interglacial is missing today. Diamond Lakes in California was dominated by pine, fir, grass, sagebrush, salt bush, and mustard plants during the Pleistocene. The Florida sites were grasslands, woodlands, and wetlands, not too different from modern conditions.

Bison relied on grass, classified as a C-4 plant, but the study shows they also ate C-3 plants–leaves, twigs, fruit, acorns, and some herbs. Bison latifrons was especially adapted to living in open woodlands interspersed with wet meadows. This species of bison grew to enormous size in order to fight off their primary predators–big cats. B. antiquus grew to a smaller size and had to survive in harsher drier environments with more scarce resources during the coldest phase of the Ice Age. Modern bison evolved to grow to a still smaller size but could run longer distances to avoid the humans and wolves that became their primary predators.

References:

Hardy, F. ; and S. Rowland

“Stable Isotope Analysis of Fossil Bison Tooth Enamel Indicates Flexible Dietary Ecology Across Pleistocene North America”

Quaternary Science Review 33 2024

https://www.sciencedirect.com/science/article/abs/pii/S0277379124002427

See also

Froese, D. ; M. Stiller, P. Heintzman, B. Shapiro

“Fossil and Genomic Evidence Constrains the Timing of Bison Arrival in North America”

PNAS 114 (13) 2017

https://www.pnas.org/doi/full/10.1073/pnas.1620754114

Taiwanese fishermen occasionally catch Pleistocene-aged animal bones in their nets when they drag them on the bottom of the Taiwan Strait. During Ice Ages the Taiwan Strait was above sea level, and it hosted a variety of extant and extinct species including straight-tusked elephant, rhino, water buffalo, horse, scimitar-toothed cat, tiger, racoon dog, human, alligator, and pond turtle. The human specimen found by fishermen was a single jawbone from an unidentified species of man. During phases of low sea levels a land bridge emerges that connects Taiwan with mainland Asia, and accordingly the island shares much of its fauna with Asia. Animal bones found in fishermen’s nets here date to between 750,000 years ago to 1,000 years ago, but the younger specimens include gray whales and right whales that date to more recent times when the Taiwan Strait became submerged. Today, the largest species of mammals on Taiwan include sambar deer and Asian black bear.

During Ice Ages Taiwan was connected to mainland Asia due to lower sea levels.

Map showing where straight-tusked elephant remains have been found on Taiwan and the Taiwan Strait. From the below referenced paper.

Scientists recently used 15 specimens of straight-tusked elephants found in fishermen’s nets and at fossil localities on land to estimate the size of this extinct species. They refer to this species as Palaeoloxodon sp., but other papers refer to the species of elephant that formerly lived on Taiwan as Palaeoloxodon huaihoensis. The status of this species must be uncertain. Based on the size of the leg bones and skulls, scientists estimated the straight-tusked elephants that lived on Taiwan and the Taiwan Strait when it was above sea level were enormous. They were on average 21% taller than modern day African elephants (Loxodonta africanus, L. cyclotis), and they weighed twice as much, exceeding 20,000 pounds. But they were not the largest species of elephant of all time. That distinction belongs to the extinct Asian straight-tusked elephant (P. namidicus), a giant that reached weights of 32,000 pounds. There were 2 other species of straight-tusked elephants that also grew quite large–the Eurasian straight-tusked elephant (P. antiquus) and the African straight-tusked elephant (P. recki).

Images of different elephant species comparing them in size. From the below referenced paper. The species of straight-tusked elephant that lived in Taiwan weighed over 20,000 pounds on average. P. namidicus weighed 32,000 pounds. By contrast the average African elephant weighs 10,000 pounds.

Computer generated image of a straight-tusked elephant.

Straight-tusked elephants lived in semi-tropical to warm temperate climates. Their ranges shrank during Ice Ages and in northern regions they were replaced by smaller but cold-adapted wooly mammoths. Straight-tusked elephants survived in thermal refuges during Ice Ages, and some lived on Mediterranean islands where they evolved into dwarf species. Humans likely hunted them to extinction when their ranges became more restricted. Evidence suggests they preferred mixed woodland and grassland environments. To reach such prodigious sizes they surely required a tremendous quantity of forage.

Reference:

Biswas, D. ; C. Change and C. Tsai

“Land of the Giants: Body Mass Estimation of Palaeoloxodon from the Pleistocene of Taiwan”

Quaternary Science Review 336 2024